FR2528194A1 - SCANNING KEYBOARD CIRCUIT WITH MICROPROCESSOR - Google Patents

Abstract

SCAN KEYBOARD CIRCUIT INCLUDING A VOLTAGE DIVIDER HAVING A PLURALITY OF RESISTORS R3, R9 CONNECTED IN SERIES, WITH TAPES BETWEEN THEM, TO GIVE BIRTH TO A PLURALITY OF GRADUATED TENSIONS AT THE TAP LEVEL. A COMPARATOR 1 HAVING A FIRST AND A SECOND INPUT IS USED TO GENERATE A SIGNAL WHEN A COINCIDENCE OCCURS BETWEEN THE VOLTAGES APPLIED TO THE INPUT TERMINALS. A PLURALITY OF MANUAL KEYS S1, S7 ARE CONNECTED TO THE SOCKETS TO SELECTIVELY APPLY THE GRADUATED VOLTAGES TO THE FIRST INPUT TERMINAL OF THE COMPARATOR. A CONTROL CIRCUIT 4 GENERATES AND APPLIES A SERIES OF CYCLIC WAVE SHAPES WITH A VARIABLE REFERENCE VOLTAGE IN TIME TO THE SECOND INPUT OF THE COMPARATOR. IN RESPONSE TO THE COINCIDENCE SIGNAL, A DATA REPRESENTATIVE OF THE INSTANT VALUE OF THE REFERENCE VOLTAGE IS STORED IN A MEMORY AND COMPARED TO A DATA GENERATED LATER, TO CHECK THAT ONE OF THE KEYS HAS BEEN ACTED WHEN A COINCIDENCE HAS BEEN ACTED. PRODUCED. IN THE EVENT OF NON-COIDENCE, THE CONTROL CIRCUIT DETECTS THE MOMENT WHEN THE MOST RECENT DATA IS GREATER THAN THE PREVIOUS DATA, TO CHECK THAT THE OPERATED BUTTON HAS BEEN CUT.

Description

1 -

  SCANNING KEYBOARD CIRCUIT WITH MICROPROCESSOR

  The invention relates to a circuit used to identify one by one of the manual keys and to detect their operating state. It relates to a keyboard circuit which

  explore a row of key switches, to identify

  the key pressed by comparing a key identification voltage with a variable reference, represented by

  data stored in memory In particular, the circuit

  cooked eliminates the inconvenience caused by iden-

  tification of keys having indefinite amplitudes which are generated by the progressively increasing contact resistance at the instant when the key switch is

released during a cut.

  A known keyboard circuit with microprocessor includes

  a voltage divider comprising a plurality of resistors

  tances connected in series, with sockets between resistors

  successive tations A network of manually operated unlocked key switches are connected to the respective sockets to produce a plurality of voltages

  graduated respectively identifying the particular functions

  touch switch switches When any of the switches are pressed, an identification voltage

  corresponding key is applied to the non-inverting input

  threshold of a comparator, whose inverting input receives a 2 - reference voltage having a stepped waveform, which

  is regenerated cyclically under the control of a microcal-

  When the two input voltages are compared

  the comparator generates a coincidence signal and authorizes the microcomputer to store in memory a datum representing the instantaneous value of the staircase voltage

  of reference that occurred at the time of the coinci-

  dence The same process is repeated to count the number of coincidences between the two input voltages When the value thus counted reaches a predetermined number, the microcomputer checks it as a valid indication that a key has been pressed in the operating state and provides

  a mode selection signal corresponding to a recording

  video or similar sorter, to make it work next

  a mode specified by the key in question.

  The keyboard circuit of this type is known as

  scanning discriminator, because the reference voltage

  Variable in time is used to explore sequentially-

  The voltage level of the signal given by the key pressed The key scanning operation continues during switch-on periods, so that the instant the key is released, the microcomputer detects a

  modification of the voltage supplied by the key network.

  This type of keyboard circuit is useful for applications where the network of keys is mounted as a separate unit at a location remote from the circuit which identifies the key functions, since it requires a

  small number of wires interconnecting separate units.

  However, a disadvantage arises from the fact that a voltage of undefined amplitude can arise at the terminals of the contact resistance of the key which is cut if it remains in an ambiguous position between the engaged state and the cut-off state It is therefore highly probable that the microcomputer will mistakenly identify the undefined voltage as an indication of the operation of a different key and will generate a false

mode selection signal.

  3 - The invention proposes to identify an undefined voltage level as an indication of a cut-off state, by detecting the moment when the most recent instantaneous value of the reference voltage variable over time becomes greater than the value previous instant.

  According to the invention, the keyboard circuit comprises a divi-

  voltage tester having a plurality of connected resistors

  tees in series with plugs between them, to give birth to

  sance at a plurality of graduated voltages at the taps, and a comparator having first and second input terminals generating a signal when a coincidence

  intervenes between the two respective applied voltages-

  at its two input terminals A plurality of switches

  manual key readers are connected to the sockets, to selectively apply the graduated voltages to the first comparator input terminal, in response to operation

  of one of said key switches A circuit of com-

  mande generates a series of cyclic waveforms of reference variable in time, which it applies to the second input terminal of the comparator and, in response to the intervention of the coincidence signal, stores in the memory a data representing the instantaneous value of the time-varying reference voltage The circuit

  command detects a coincidence between the data which represents

  feel the instantaneous value of a reference voltage variable in time generated subsequently and the data which is stored in the memory and checks that one of the

  key switches have been pressed The process below

  above continues to monitor a voltage change at the first comparator input terminal, to detect the instant when the key is cut The control circuit checks this cut-off state by detecting the moment when the

  most recent data becomes greater than the previous data

duly stored.

  The invention will be better understood using the description below.

  after. 4- In the accompanying drawing: FIG. 1 schematically represents a keyboard circuit according to the invention;

  Figure 2 shows the waveforms of a greater

  of pulse trains and a voltage of

  staircase reference from these pulse trains

sions;

  Figure 3 is a flowchart illustrating the ins-

  programmed tructions executed by the microcal-

  culateur of Figure 1, according to an embodiment

  cution of the invention; FIG. 4 represents the waveforms intended to illustrate the operation of the invention; and

  Figure 5 is a flowchart showing the ins-

  programmed calculations of the microcomputer,

even to a variant.

  Referring to Figure 1, there is shown a scanning keyboard circuit with microprocessor, in which a network of manual keys Sl to 57 of the unlocked type are respectively connected, at their first terminals, to sockets of a divider voltage comprising a series of resistors R 3 to R 9 connected to ground by one of their

  ends More precisely, the network of keys is

  intended to be used in a video tape recorder in which the keys Sl and 52 have their second terminals connected to each other and to the first terminal of the key 53, while the second terminals of the keys 53 to 57 are coupled together to a junction point 5 between resistors R1 and R 2 The keys Sl and 52 have special functions which are used only when the key 53 is pressed. -

  A voltage comparator 1 has a non-inverting input.

  threshold coupled, through resistance R 2, to junction point 5 When all the keys remain in the off state, the voltage which arises at junction point 5 is determined by a voltage transmitted through resistance Rl from d a Vcc supply To the inverting input of comparator 1 is applied a reference voltage

  composed of a series of stepped waveforms, from

  from a digital to analog converter 4 of the scale type When the two inputs of comparator 1 are in

  Coincidentally, a signal is applied to a microcomputer 2.

  This is of any traditional type and comprises a microprocessor, a read-only memory, a random access memory and a certain number of counters and registers which have all been omitted, for simplicity, because the invention does not

  does not concern the material structure of the microcomputer.

  As will be described in more detail below, the microcomputer 2 executes programmed instructions to generate a series of reference data which are

  translated into a plurality of pulse trains of

  different frequencies, as indicated by the waveforms a, b, c and d, in Figure 2 They are applied to terminals 3 a

  at 3 d and, from there, to the respective sockets of the network of resis-

  tances in scale 4, where the pulses are combined to generate a staircase voltage represented at e in FIG. 2 The highest value of this voltage emax is slightly lower than the supply voltage Vcc, but slightly higher than the voltage which would be generated in

  response to the operation of the key switch 57.

  When any of the keys 51, 57 is pressed, an identification voltage of this key is applied to

  the non-inverting input of comparator 1 and compared succeeds

  each of the variable voltages in steps.

  When the compared voltages coincide, comparator 1 sends a pulse to microcomputer 2, to authorize it to store the reference data which has occurred at

the instant of comparison.

6 -

  A more precise description of how the microcal-

  culateur 2 is given with reference to the flowchart of the

figure 3.

  In FIG. 3, it can be seen that the execution of the program begins with an operation illustrated by block 10 and in which the microcomputer applies pulses to the terminals 3 a to 3 d which correspond with the highest value e max of the voltage in steps, to check if all the keys are in the cut state If this is the case, comparator 1 generates a low level voltage and the microprocessor detects this as indicating a state "all keys cut" and progresses up to operation 11; if this is not so, it goes to operation 12 In operation 11, a memory location is addressed to store data representing a given voltage, which is greater than

  any of the key identification voltages.

  In operation 12, the microprocessor generates a data R corresponding to a voltage step e of the staircase reference, which is applied, in the form of the pulses

  mentioned above, to the digital-to-analog converter

  gic 4, and goes to an operation 13 to check if a coincidence signal is generated by the comparator 1 If

  there is no coincidence, an operation 14 will be executed

  cut so as to increment a reference step counter a by one, to return to operation 12 and increment the reference voltage in steps by one If coincidence is detected, the microprocessor stores the value a of the reference step into a new

  Mnew memory location during operation 15.

  In an operation 16 a comparison is made between the value A and the previous value A now stored in the old memory location Mold If the key remains pressed, a check is made, during an operation 17, to see if the coincidence has occurred ten times in a row and, if not, a coincidence counter C is incremented by one in operation 18 and program execution returns to operation 12 to reproduce the above process If the coincidence occurs 7 - ten times, the microprocessor recognizes it as a valid indication that a key has been pressed in the engaged state and issues a mode selection signal to a circuit specified by the value A which represents the particular function of the key pressed (operation 19). If no coincidence occurs during operation 16, the microprocessor exits until operation 20 to

  check if the value A is smaller than the value A pre-

  yield and, if so, the memory Mnew is updated with the value A in operation 21 and the coincidence counter C is recalled in step 22 before returning to

  step 12 If the value A is greater than the previous value

  dente, an operation 23 is executed to deliver a signal

  or cancel the mode selection signal.

  Figure 4 shows the operation of the device.

  sitive in the form of a time diagram.

  Assuming that key 53 is pressed at time t 1, which causes the voltage at the non-inverting input of comparator 1 to drop rapidly, from the source voltage Vcc to a determined fraction of Vcc speak

  ratio (R 3 + R 4 + R 5) / (Rl + R 4 + R 5) As a result of the resistance

  tance of clean contact of key 53, the voltage does not decrease rapidly to the calculated level indicated by a dotted line 25 and follows a waveform 26 represented by a solid line, so that it remains briefly at a level corresponding to the value which would be given by the key 54 Consequently, a first coincidence pulse 27 occurs at the instant

  o a reference voltage 28 reaches a discrete level 6.

  The voltage decreases progressively and reaches the calculated value A second coincidence pulse 29 occurs when a subsequent reference voltage 30 reaches a level 5 If the voltage remains at the calculated value, the maximum value of the reference voltages which occur during the next interval is stationed at level 5 and the coincidence counter C can be incremented up to a value 10 which authorizes the microprocessor to generate a

  switch-on signal in step 19.

  8 - If the key switch 53 is released at time t 2, the voltage at the non-inverting input of comparator 1 should normally increase rapidly to the high cut-off level, as indicated in 31 a However , if the finger remains briefly on the button 53, so that the latter takes an intermediate position between switching on and off, the contact resistance of 53 increases and, consequently, a voltage of undefined amplitude, as indicated at 31, is generated at the non-inverting input of comparator 1 This voltage 31 would correspond to a level which would be reached if a key 54 was pressed A reference voltage 32 having a step level 6 is thus generated in response to a coincidence pulse 33 and the microprocessor comes out

  from step 16 to go to step 20.

  According to the keyboard circuit of the prior art, the micro-

  processor would exit step 16 to go directly to step 21 and update the memory by means of data corresponding to the value of the undefined voltage, to execute a loop passing through steps 12 to 18 and recognize the new status as an indication that the key 54 has been pressed and thus deliver a false signal

control.

  However, due to the existence of steps 20 and 23, the

  voltage change from minimum level 25 to inde- pendent level

  finite 31 allows the microprocessor to deviate from the key exploration loop to authorize the production of a

valid cutoff signal.

  Figure 5 is a variant of the flow diagram of Figure

  3, further comprising operations 40 and 42, for repro-

  duction operation 20 so as to ensure that the voltage

  indefinite is present for a certain period More pre-

  briefly, after having made a decision "NO" to the operation, the microcomputer goes through steps 40 and 41 by checking the value of the account in a second coincidence counter D and by incrementing it by one unit to return to the step 12 If the indefinite tension continues, the execution of the program comes again to step 20 and 9 - reproduces operations 40 and 41 When D = O is detected in operation 40, the coincidence counter D is recalled to zero in operation 42 before the execution of

operation 23.

-

Claims (2)

Patent claims   1 keyboard circuit comprising a voltage divider having a plurality of resistors (R 3 R 9) connected in series, with taps between them, to generate a plurality of graduated voltages at said taps; a comparator (1) having first and second input terminals, used to generate a signal when a coincidence occurs between the voltages applied to its first and second terminals respectively entry.   a plurality of key switches (SI 57)   manually operated, connected to said sockets for appli-   selectively quering said graduated voltages at said input terminal in response to the operation of a key switch; and   control means (4) for generating and applying   quer a series of recycling waveforms of a reference voltage variable in time at said second terminal   input and responding to the arrival of said coincidence signal   dence, to store in a memory a datum representing   the instantaneous value of said reference voltage varies   ble over time, repeatedly detect a corner   cidence between the data which represents the instantaneous value of a reference voltage variable in time generated subsequently and the data stored in said memory, to verify that one of the key switches has been actuated and detecting the moment when the instantaneous value last mentioned is greater than the last mentioned stored data to verify that the   button switch pressed has been turned off.   2 keyboard circuit according to claim 1, characterized in that the time-varying reference voltage is constituted by a series of waveforms in staircase.   il - 3 keyboard circuit according to claim 1, characterized in that the control means comprises a digital-analog converter (4) having an output connected to the second comparator input terminal (1) and a microcomputer (2) programmed to execute the following operations: a) Production of a reference data representing the   instantaneous value of a staircase voltage and appli-   cation of this data at the input of the conversion means   sion to cause the latter to generate one of said instantaneous values; b) Detection of the comparator coincidence output;   c) If the coincidence output is not detected, repro-   duction of operaton (a) and (b); d) If the coincidence output is detected, storing data representing said instantaneous value in a different location from said memory; e) Detection of a coincidence between the data stored in   last place in memory and prior data-   stored; f) If this coincidence is detected, detection of the fact that the number of interventions of said coincidence reaches a predetermined value, to verify that one of the key switches has been activated and detection of the fact that said predetermined value has not was reached to return to operation (a); and g) If said coincidence is not detected, detection of the moment when the most recently stored data is greater than the previously stored data, to verify that the key pressed has been cut and detection of the moment when the most stored data   recently is less than the data previously stored   to return to operation (a).   12 - 4 keyboard circuit according to claim 3, characterized in that the operation g, further comprises: if the most recently stored data is greater than the previously stored data, the detection of the moment where the number of interventions of this condition reaches a predetermined value to verify that the key pressed has been cut.